Field of Invention
The present invention relates to an ion guiding device and an ion guiding method, and particularly relates to an ion guiding device and an ion guiding method in which the ion flow injected is bunched at a certain gas pressure and then ejected in a pulsed manner.
Description of Related Arts
In a mass spectrometer or an ion mobility spectrometer, for an ion analyzer used in a pulsed manner, the required ion flow must be in pulses instead of continuous. For example, for a time-of-flight mass analyzer, the ion flow entering a flight tube must be in pulses to match with an acceleration voltage of pulses. This is the reason why the time-of-flight mass spectrometer is always used together with a pulsed laser desorption ionization source, since the latter one can generate a pulsed ion flow. For the ion mobility spectrometer, it is also required that a pulsed ion flow enters a drift tube to match with a pulsed drift voltage. However, in many cases, the ion flow obtained from an ion source (for example, the most widely used electrospray ion source and electron impact ion source) is continuous or semi-continuous, such ion sources cannot be directly used together with the pulsed ion analyzer, and an ion bunching device is usually necessary to turn the continuous ion flow to a pulsed ion flow. However, the current ion bunching device generally loses sensitivity thereof and requires complicated operation timing, so that a power supply and a control system thereof are complicated as well.
For example, for the time-of-flight mass spectrometer or the ion mobility spectrometer, a conventional ion bunching device is a method proposed by Brenton et al. in “Rapid Commun. Mass Spectrom. 2007; 21: 3093”, in which an ion gate is simply disposed, the ion gate is usually in a closed state, and when ion pulses are required, the ion gate is opened rapidly and then closed rapidly, so as to generate a very short ion pulse and eject the ion pulse, this is equivalent to “slice” the ion flow. However, a large amount of ions between two “slices” will be lost by using this method, resulting in reduced sensitivity of instrument.
To improve the utilization of ions as much as possible, it is proposed by Chernushevich in “Eur. J. Mass Spectrom. 2000; 6: 471” and Hashimoto in “J. Am. Soc. Mass Spectrom. 2006; 17: 1669” that a multipole rod applied with a radio frequency (RF) voltage may be used to trap ions temporarily, this method can effectively improve the “duty cycle” of ions being leading to the time-of-flight mass analyzer; however, this method essentially uses an ion gate and still needs to operate the voltage according to certain timing, and a power supply and a control system that are required to be provided are also complicated accordingly.
Further, there are some methods for forming a well-bunched ion packet. For example, the electric field in space where the ion flow is located is divided into several segments for respective configuration, ions are decelerated or reversed in a front segment and accelerated in a post segment, so that ions are adjacent to each other to form an ion pack; or, a deceleration region is disposed at a certain segment through which ions pass, when the ion flow passes through, an electric field of the deceleration region is removed rapidly, such that ions in a front segment of the ion flow are decelerated for a longer time to have a greatly reduced speed, and are caught up by ions in a post segment, so that the ion flow is compressed into a packet. However, these manners have the following obvious defects: for example, not only a high-speed operation timing is required, but also different space potentials need to be disposed, which is complicated in implementation; moreover, these manners all have energy selectivity, and cannot well bunch ions having a relative large incident energy difference; further, these manners all need a high vacuum degree to ensure the stability of an ion optical system, and if the vacuum degree is low, ions colliding with background gas molecules cause the ions' movement in a mobility dependence, and ions having different mobilities will disturb the pulse sequence.
U.S. Pat. No. 6,812,453, proposes an ion guiding device driven by using a traveling wave of a direct current voltage. This device can not only cool and bunch the ion flow in a relative broader gas pressure range into a pulse ion flow, but also obtain a substantial same speed when ions are ejected from the device. However, in this device, voltages of electrodes need to be adjusted separately, and therefore, a circuit and a control system thereof are complicated.